MathDB
Projections of points and lines

Source: Baltic Way 2007

November 30, 2010
geometry proposedgeometry

Problem Statement

Let t1,t2,,tkt_1,t_2,\ldots,t_k be different straight lines in space, where k>1k>1. Prove that points PiP_i on tit_i, i=1,,ki=1,\ldots,k, exist such that Pi+1P_{i+1} is the projection of PiP_i on ti+1t_{i+1} for i=1,,k1i=1,\ldots,k-1, and P1P_1 is the projection of PkP_k on t1t_1.